1. Field of the Invention
The present invention relates to an oscillator module and a communications device using the same and, more particularly, to an oscillator module used in an ultra-low power or low-power radio device, and a communications device using the same.
2. Description of the Related Art
Recently, there has been an increase in the use of communications devices using ultra-low power or low-power and remote control systems, such as in keyless entry. An oscillator module which maintains stable and high-precision oscillation over a long period of time is used as a signal source in these systems.
FIG. 7 shows a block diagram of a conventional oscillator module. An oscillator module 1 comprises a resonator 2 and a circuit for oscillation 3, which are connected together in a loop and hermetically sealed in a package 4. The package 4 is provided with external terminals 5 and 6 for power input and signal output, and these are connected to the circuit for oscillation 3. The oscillator module 1 functions as a signal source.
Furthermore, FIG. 8 shows a block diagram of another conventional oscillator module, disclosed in Japanese Unexamined Patent Publication No. 9-162643. In FIG. 8, identical or similar members to those of FIG. 7 are designated by the same reference numerals, and a detailed explanation of these members are omitted.
In the oscillator module 10 shown in FIG. 8, the resonator 2 and the circuit for oscillation 3 are not connected to one another inside the package 4. Instead, the resonator 2 is connected to external terminals 11 and 12, provided at the package 4, and the circuit for oscillation 3 is connected to external terminals 5 and 6, also provided at the package 4.
In the oscillator module 10, the resonator 2 and the circuit for oscillation 3 are independent of each other (i.e., they are separately arranged), and it is possible to measure their characteristics while they are sealed in the package 4. However, the module cannot function as an oscillator in this state. Therefore, the external terminals 11 and 12 are connected outside the package 4 to the external terminals 5 and 6, respectively, by external other wires 13 and 14. Thus, whereby the resonator 2 and the circuit for oscillation 3 form an oscillator loop and the oscillator module 10 functions as a signal source in the same way as the oscillator module 1.
There are cases where the characteristics of an oscillator module change when it is hermetically sealed in a package.
However, in the oscillator module 1, although it is possible to measure the oscillation characteristics after sealing it in the package 4, it is not possible to measure the oscillation margin, since this requires a measuring device to be individually connected to both the resonator 2 and the circuit for oscillation 3, which form the oscillator, and also between the resonator 2 and the circuit for oscillation 3 (at a point in the oscillator loop). Consequently, when the conditions under which the oscillator module 1 oscillates cannot be detected in advance (even when such conditions are very strict). When the oscillator module 1 is incorporated in an electronic device, there is a possibility of malfunction, such as the oscillator ceasing oscillation after being combined with other components.
In the oscillator module 10, the resonator 2 and the circuit for oscillation 3 are independent from each other (i.e., not connected within the package 4) and, therefore, it is possible to measure the resonator 2 and the circuit for oscillation 3 individually. It is also possible to measure the oscillation margin using other connection wires. However, since the resonator 2 and the circuit for oscillation 3 are provided independently, there is a problem in that the number of external wires is increased, making the package larger by a proportionate amount and increasing the cost of the package. There is a further problem in that the increased number of external wires prevents the oscillator from being made small-scale. Moreover, there is a problem in that the external wires act as part of a phase circuit of the oscillation loop, and variation in the lengths of the multiple external wires increases complexity, resulting in loss of stability of the oscillation frequency.